Waterborne curable resin compositions can cope with environmental problems due to the advantage of being waterborne and exhibit various physical properties because of curability. Thus, the resin compositions are suitably used in various applications that require formation of coats having various physical properties by curing, for example, by means of ultraviolet rays, and the like. Such waterborne types of curable resin compositions include a water dispersion type (also called an emulsion type) and a water-soluble type. The water dispersion type is produced by water dispersing an ultraviolet-ray (UV) resin with an activator and used. In regard to dispersion stability, the type has a property of tending to agglutinate before irradiation of ultraviolet rays. As the water-soluble type, a water soluble type of a UV curable resin is known. The water-soluble type is, however, hydrolysable and unstable, and is low in water resistance due to a lot of hydrophilic groups such as acid groups and polyethylene glycol (PEG) groups. In addition, the water-soluble type having PEG groups, and the like tends to be soft when cured, so the type may spoil the advantage of stiff coat formation due to UV curing.
As conventional UV curable paint compositions, “Design of Waterborne UV/EB Curable Resins” written by Hiroshi Sawada, pp. 35-43, 2001 discloses a UV/EB curable resin in which the fundamental constitution is made of a polymerizable oligomer/reactive diluent/light initiator, and “Water-based UV Curable Inks” written by Michio Takao, Fine Chemicals, No. 1, Vol. 34, pp. 52-57, January, 2005 discloses a water dispersed system made by use of a UV curable resin as an activator.
Furthermore, as the light-sensitive compositions containing water as a solvent or dispersant, Japanese Patent Laid-Open No. 5-9407, p. 1 discloses a light-sensitive composition containing as a binding agent at least a water-soluble, solid, curable film-forming polymer, a water-soluble light-polymerizable acrylate, an oligomer, or a light initiator compound, and Japanese Patent Laid-Open No. 9-302266, pp. 1-2 discloses a water base light-sensitive coating composition made by blending a water base resin dispersant with a light-sensitive polymer or light-sensitive monomer.
When the fundamental constitution is made to be a polymerizable oligomer/reactive diluent/light initiator like the above curable resins, the reactive diluent does not vapor after curing. The composition can substantially be made to be a non-solvent composition and thus is advantageous from the viewpoint of environmental protection measures. However, a composition diluted only with a reactive diluent cannot improve various physical properties of the cured material in balance.
Additionally, in an emulsion that is usually used, a soft cured material does not need a solvent as a film-forming assistant, but a stiff cured material with improved physical properties such as stain resistance needs a solvent as a film-forming assistant such as 2,2,4-trimethyl-1,3-pentadiolmonoisobutyrate. As such, a composition having a polymerizable oligomer/reactive diluent/light initiator as the fundamental constitution or an emulsion system (or only emulsion/film-forming assistant) is advantageous for environmental problems, but cannot promote performance balance in various physical properties. Accordingly, a resin that forms a coat improved in basic performance and can suitably be applied to a variety of applications has been required.